Any discussion of the background art throughout the specification should in no way be considered as an admission that such background art is prior art, nor that such background art is widely known or forms part of the common general knowledge in the field.
Identification of on-ground or near-ground discrete objects is a common task for specialist scientists and engineers. As used herein, the term “on-ground object” refers to localised geographical objects at the ground level (i.e. that is connected to or part of the ground) e.g. terrain and/or contour features. Examples of such objects include natural landforms such as drumlins (a ‘little ridge’, typically an elongated hill in the shape of an inverted spoon or half-buried egg formed by glacial ice acting on underlying unconsolidated till or ground moraine); ecological features such as termite mounds; archaeological features such as tumuli (i.e. mounds of earth), craters, and stones raised over a grave or graves. Tumuli are also known as barrows, burial mounds, Hügelgrab or kurgans). As used herein, the term “near-ground object” refers to objects, for example trees, spinifex, salt bush, structural or man-made objects such as buildings or vehicles that, generally, are above the ground level or extend from ground level, and are usually located on or resting on the ground. Examples of such objects include built objects such as buildings, water tanks or motor vehicles.
The identification of on-ground or near-ground discrete objects may be undertaken by ground-based observational field survey; or by remote sensing techniques using electromagnetic energy (e.g. laser energy), including energy in the wavelengths of light visible to human eyes. Various types of survey techniques may be combined to improve the likelihood of detection of on-ground or near-ground objects. These techniques include the use of data acquired by techniques such as, for example, Light Detection and Ranging (LiDAR).
LiDAR data is collected by emission of a laser from an instrument typically mounted on the ground or in an aircraft. A LiDAR detection unit typically is situated in the same instrument as the emitter. The LiDAR unit transmits and detects laser pulses which are reflected off objects on the ground or in the air, including: soil, rocks, leaves, branches, vehicles, buildings, birds, etc. The LiDAR unit measures the time, direction and strength of each reflected laser pulse and the position, velocity and orientation of any transporting vehicle are calculated to determine the geographical position of the reflected laser pulse.
Executing the identification of on-ground or near-ground discrete objects using LiDAR over a wide area requires substantial effort where the number of such objects is large, or where the area to be examined is large. In addition, even when LiDAR data is used for survey purposes, where the area to be examined for such objects is inaccessible by vehicle, it may be infeasible to undertake extensive field calibration of any objects identified in LiDAR data.
An additional difficulty with the use of remotely-sensed LiDAR data is that it may be used only to identify objects on the ground that may adequately be distinguished in the available data from surrounding materials and features, which may be considered as ‘noise’ within the data.
Given the problems identified above, there is a need for an improved technique for identification of on-ground or near-ground discrete objects from remotely-sensed data such as LiDAR.